First things first – the knowledge is a test that all London taxi drivers have to pass to get their hackney carriage (taxi) licence. In the test they have to answer questions about 320 routes, landmarks and street names. Doesn’t sound so bad right?

Well…unlike US cities which are laid out in a friendly and easy to remember grid, London as a city grew organically and therefore it’s streets are far from uniform and follow no real pattern. Those 320 routes cover a staggering 25,000 streets and just under 20,000 landmark, all within a 6-mile radius of Charing Cross station.

Not only does the test cover routes and landmarks, but participants have to use their knowledge of these routes to advice the fastest routes for their passengers. The process of learning these routes on average takes 3-4 years and is equivalent to an undergraduate degree not only in length, but in intensity. Only half actually pass the test and go on to be London cabbies.

Could you remember 25,000 streets and 20,000 landmarks? It seems like it would take a special kind of person with an incredible memory.

Researchers at the University College of London published a report in Current Biology journal which explored the effects of memorising a disorganised system on the brain. To do this they followed the progress of 79 would-be cabbies while they were training to pass “the knowledge”. Throughout the learning process, the brains of the participants were mapped by MRI scanners, giving the researchers an idea of how their studies were affecting their brains.

Of the 79 students, only 39 passed and went on to become cabbies. What the researchers discovered was ground-breaking. They compared the MRI scans of the 39 who passed with those who had failed and found that the grey matter in the hippocampus had actually grown over time. The students who had failed didn’t show any similar brain development.

Thanks to the way we evolved as nomadic hunter-gatherers, our spatial memories are particularly strong and the knowledge is the perfect demonstration of our ability to use and improve our spatial memory.

When compared with non-cabbies, cabbies drastically outperformed on memory tests involving landmarks and spatially-based tests. However, they had no similar advantage when taking tests involving visual or other types of memory.

The implications of this study were huge, particularly in the adult education industry as the study demonstrated that the brain is able to adapt perfectly to learning new tasks and doing so can even change the physical structure of the brain.

These findings are in line with ideas posed by Robert Greene in his book Mastery. Throughout the book, Greene explains how after 10,000 hours of successful deliberate practice, not only does one master a subject, but the physical structure of the brain is altered so that insights which would normally take hours of thought and reflection could be produced in moments.

The downside was that these new cells follow the “use it or lose it” rule. Retired cabbies who stop using their spatial knowledge will find that their hippocampus will shrink back to normal size over time